The Space Shuttle's heat shield was the program's Achille's heal. It was fragile, and time consuming to repair and maintain. The need to manually inspect each tile after each mission caused the space shuttle operations to drop from an initially planned one mission per week to a point where NASA struggled to have one mission per month. Since the limitations of the system began to become apparent before the first shuttle mission even flew, and since we're talking about something on the outside, that could theoretically be replaced without tearing the entire shuttle apart, does anyone know if there was any consideration to developing a replacement within the shuttle's lifetime?

I don't know about that. What i can say based on what i remember from some readings was that the shuttle itself was never supposed to be the size that it ultimately became. If you look at the X-37b, and about double its size that would have been the original shuttle. What we got was the result of needing more money for the project, so NASA opened up the project to the DOD (the Air Force), and it would have been only funded with them if it had the heavy lift capability. With that in mind, the shuttle grew in size to support.

IF the shuttle were smaller, one could wager that the tile issue wouldn't have been so great as the surface area needed to cover would have been much less.

A replacement for the heat shield system, I don't know of. However there was a planned, and mostly completed, replacement for the entire Space Shuttle, called the X-33/Venture Star.

I've done a fair amount of reading on the after-incident reports of both Challenger and Columbia. And as far as Columbia goes, in my opinion, I believe that the hardware takes far too much blame where the personnel (human negligence, not human error) should. Long story short, the risks to the thermal shielding were well known for years and many missions before Columbia. I believe that people were more concerned about keeping their jobs, rather than taking precautions that would have slowed the program even more, or shut it down potentially. And then there are the contractor production and payload revenue influences.

Regardless of what I say, the professional review board for the Columbia destruction put most of the blame on NASA's risk management and flawed operational "order of battle" (my paraphrase, not theirs).

The damage was known long before re-entry. No one knows if the crew could have been saved, but it is known that we didn't try. We had the ISS in orbit as a potential safe haven. We had the Russians to bring them back from the ISS if we could not get another shuttle ready in time. As galling as it may have been to ask for help, it's preferable to crew death. I think if we had shown the resolve that we did with the Apollo 13 accident, that we could have saved lives. Some egos and maybe some careers would have been bruised (which ended up getting bruised anyway), but that shuttle crew may have survived. Not even an attempt was made.

The Space Shuttle's heat shield was the program's Achille's heal. It was fragile, and time consuming to repair and maintain. The need to manually inspect each tile after each mission caused the space shuttle operations to drop from an initially planned one mission per week to a point where NASA struggled to have one mission per month. Since the limitations of the system began to become apparent before the first shuttle mission even flew, and since we're talking about something on the outside, that could theoretically be replaced without tearing the entire shuttle apart, does anyone know if there was any consideration to developing a replacement within the shuttle's lifetime?

The real achilles heal was having too many cooks in the kitchen.

All the stakeholders wanted something different out of the system so you got this bloated design that never really could do everything that they wanted. EDIT: but with any govt program the money was taken away to go to something else (probably defense)

At the time the tiles and other TPS materials (carbon carbon leading edges Im looking at you) were really the only option for something that didnt need to be completely replaced (ablative)

There probably was a desire to upgrade, and if you look at the newer shuttles the design did get iterated and improved to a certain degree

I actually worked on the space shuttle (RCS and OMS) at the beginning of my career, it was really fun/cool and I miss it alot, when the shuttle was finally at wheel stop and they flew Discovery over our site I cried like a baby